This is a simple version of what they call an Oyster Roast in the Carolina low country. You just put some nice plump oysters over a hot fire and when they pop open, you spoon over a little lemon butter and serve them immediately. A friend of mine, Tim Gilchrist, invented a special tool he calls a "Great Grate" which holds the oysters upright and allows you to pick up the grate instead of the individual oysters. It's really a very special tool. They are made in various sizes that can hold 6 to 30 oysters. The grate can also be used for clams. Great Grates can be purchased on line at www.greatgrate.com or by calling Great Grate at 877-768-5766. You can use any medium to large plump oysters for this recipe, but I like to use wild oysters like blue points; fancy half-shell oysters are expensive and some of their nuances are lost in the cooking. For equipment you will need a grill, grill brush and a pair of long tongs. The "Great Grate" is optional, but makes the job much easier. You will also need a 1-quart saucepan, a wooden spoon, and a whisk to make the sauce.
Scrub and rinse the oysters. Keep refrigerated until ready to grill.
To make the sauce: Pour the cream into a 1-quart saucepan and cook over low heat, whisking occasionally to prevent the cream from boiling over, until the volume is reduced by half, about 8 minutes. Increase the heat to medium and add the butter, 1 piece at a time, whisking constantly, until the sauce is shiny, emulsified, and thick enough to coat the back of a spoon. Add the lemon juice and simmer briefly. Remove the saucepan from the heat. Add the chervil or parsley and season, to taste, with salt and pepper. Keep the sauce warm until ready to serve.
Set up the oysters on the grill with the cup side down (and flat side up) or place them directly on the grill in the same fashion. Cook the oysters without turning them.
As soon as the oysters pop open, after 8 to 10 minutes, transfer them carefully with tongs to a platter (or plates) lined with a bed rock salt. If you are using a Great Grate, this won't be necessary. Use the tongs to pry off the top shells. Spoon 1 teaspoon sauce over each oyster and serve immediately.